1. Field of the Invention:
The present invention relates to a direct acting flow control valve using rolling diaphragms.
2. Description of the Prior Art:
The present flow control valve has particular application in the regulation of water flow through a condenser operating in a refrigeration system. Where the flow is relatively low a smaller valve can be used which typically employs a piston and bellows assembly movable in response to refrigerant pressure applied to the valve. Such valve bellows are made of stainless steel or other metallic material for corrosion resistance, and consequently they are relatively expensive and sometimes prone to fatigue failure. This type of valve cannot accommodate large flow rates because it does not have a sufficiently great longitudinal excursion or movement.
The typical larger valve for higher flows utilizes an indirect valve actuation system. A so-called pilot valve is used which incorporates a metal bellows responsive to fluid pressure. This applies pressure to the main valve through an arrangement of narrow pilot passages. The small longitudinal excursion or movement of the pilot valve is multiplied by the system, but the pilot passages are very susceptible to clogging with sediment and foreign matter, particularly in a marine system for regulating the flow of seawater.